It has recently been suggested in U.S. Pat. No. 3,644,305 to carry out the polymerization of acrylamide and the like by spraying an aqueous solution of the monomer with an appropriate catalyst into a blast of hot air in a spray dryer apparatus. A principal object of the foregoing process is to obtain the polymer product in the form of a substantially dry solid and thereby to avoid the substantial problems encountered in drying the thick viscous gels normally obtained in the conventional process of polymerizing water-soluble monomers in aqueous solution. It will be noted however that the above process has the drawback that relatively high proportions of peroxide catalyst must be employed in order to accomplish conversion of the monomer to polymer. The process also employs elevated temperatures for its purposes and any unreacted monomer may constitute a hazard in the vent gas.